Power generation derived from variations in the earth's natural environments is in its early stages, and several technologies have been proposed.
A large number of prior art devices seek to harness the energy of ocean waves or the tides by measuring the varying height of the water through the use of floats. The float assembly is typically tied to a mechanical device in order to store energy, or to provide kinetic energy to an electric generator. One disadvantage of this approach is that it requires a mechanical connection from the float assembly to a stable reference point, usually the ocean floor. This could only be implemented in relatively shallow water environments where the risk of an apparatus breakup would be great.
Another group of prior art devices seeks to harness tidal energy by inserting turbines in the path of tidal currents. This solution will work only in a relatively small number of locations, and necessitate a thorough understanding of all forces at these locations, along with an assumption that these forces will not change over time.
Another group of prior art devices relies on the building of reservoirs at different levels and exploiting the movement of current between reservoirs. This solution is limited to near shore construction.
A reasonable alternative to the above mentioned approaches is to employ a power generating device which is completely submerged, and does not employ floats, or otherwise need to be in contact with the water surface. This type of device normally exploits the differences in hydrostatic pressure which occur as a result of tidal, wave, or other natural activity in the ocean.
One example of a submerged wave energy power generating device is U.S. Pat. No. 4,630,440 to Meyerand. In Meyerand, a constant pressure fluid reservoir positioned on land is connected by a hose to the submerged wave machine, which consists of a water filled outer housing and a fluid filled inner flexible bladder. The housing includes an opening to the ocean which includes a turbine driving an electrical generator. In this way, variances in hydrostatic pressure caused by the waves cause a filling and collapsing of the bladder, thereby increasing and decreasing the volume of water in the housing. This causes an inflow and outflow of water from the housing through the turbine, which is caused to turn to and fro. The turbine drives a generator, creating electrical power. This arrangement must be located near the shore, limiting the size of the apparatus and the amount of power it might produce. The hose would be susceptible to the difficult weather conditions sometimes found along the seashore.
A second example is U.S. Pat. No. 5,349,819 to Margittai. This apparatus employs a pump driven by hydrostatic pressure on the downside and a flexible member on the upside to drive pressurized water through 3 check valves to a collection tank for later use in driving a turbine. In this arrangement the pump plunger must move vertically and water flow takes place in one direction only. The need for a sealed air chamber would make this device difficult to produce and operate at significant depths.
Most prior art focuses on exploiting one particular phenomenon to the exclusion of others. In the case of the harnessing of ocean energy, for example, very few solutions, if any, seek to incorporate lower frequency tidal and higher frequency wave effects. Most proposed solutions are also applicable only to the particular environments for which they were originally designed.